A Japanese boy developed febrile seizures and gait disturbance at 2 years of age and dysarthria a year later. He had generalized tonic-clonic seizures once or twice a year from the age of 4 years. Brain computed tomography (CT) showed symmetric low-density areas in the white matter of the frontal lobes. However, abnormal CT findings fluctuated occasionally, with no apparent change in clinical manifestations. Clinical evaluation at 9 years of age revealed hyper-reflexia, psychomotor retardation, megalencephaly, and slurred nasal speech. Magnetic resonance imaging showed white matter abnormalities, predominantly in the frontal lobes. He was a heterozygote of the Arg239Cys mutation of the glial fibrillary acidic protein gene and was diagnosed with Alexander's disease. Fluctuation of CT findings in white matter may reflect blood-brain barrier dysfunction in Alexander's disease.